This invention relates to methods of separating mixtures of metals from each other in aqueous solution. In particular, methods for separating mixtures at least one Group VIII metal from at least one metal from Group V and Group VI to form single metal salt solutions.
Many hydrocarbon feedstocks contain high percentages of metals, particularly iron, nickel and vanadium or tungsten. These metals tend to deposit on the surfaces of hydroprocessing catalysts which contain catalytic hydroprocessing metals, frequently cobalt or nickel and molybdenum or tungsten. When the hydroprocessing catalysts no longer give desired conversion rates, due in part to metals deposits plugging the catalyst's pores, they are replaced and disposed of. Because of growing shortages of petroleum in the world, refiners must use feedstocks that contain larger amounts of metals than those feedstocks heretofore used resulting in more spent catalysts. Recycling spent catalysts would also reduce problems attendant with disposal of spent catalysts.
Spent catalysts containing large quantities of both catalytic metals and metals removed from the hydrocarbon stream, can be viewed as high grade ores of nickel, cobalt, molybdenum and vanadium. Recycling cobalt, a particularly expensive metal, would lessen the cost of these catalysts.
Methods are known for leaching the metals from spent catalysts, for example, an ammonia and ammonium salt leach in aqueous liquid removes nickel, cobalt, molybdenum and vanadium but leaves behind both the catalyst support and iron. However, once in solution, cobalt, molybdenum, vanadium and nickel need to be separated from each other in relatively pure form.